Bug: Nested object values in blocks can reset on subsequent saves

[bobbwal]

Summary

Nested object field values inside block data can be lost or reset after a subsequent save, even when the second edit is
unrelated.

Current behavior

In block-based content (for example, a Hero block with CTA objects), values inside nested objects may save correctly the
first time, but then reset on a later save.
Example: CTA button style set to secondary reverts to primary after editing another field and saving again.

Expected behavior

Nested object values should persist unchanged across repeated edits/saves unless explicitly modified.

Affected area

• Admin content form serialization for structured/nested object and array fields within blocks.

Repro steps

1. Create or edit content using a blocks field (e.g. Hero block).
2. Set nested object values (e.g. CTA style = secondary, CTA link settings).
3. Save.
4. Reopen content, change an unrelated field (e.g. title), save again.
5. Observe nested object values may reset.

Notes

• This appears in serialization/readback logic for structured fields in the admin form, not in frontend rendering.
• Observed with nested CTA object fields in Hero blocks, but potentially relevant to other nested structured shapes.